The scale effect, which is a common feature in tests of mechanical properties of rocks, refers to a phenomenon in which a certain characteristic varies with different scales of an object. The characteristic that the mechanical properties of rocks decrease with the increase of the sample scale exists not only in the tensile, compressive, shear, elastic modulus and rheological properties of rocks, but also in the shear characteristics of rock joints. In order to study the shear strength-scale effect of a rock joint, a scale effect test system is required to complete the tests of the rock joint, and to establish direct shear tests for rock joint samples of different scales under same load stress level.
At present, among direct shear test apparatuses for the scale effect of a rock joint are, D U Shigui proposed testing machines for shear strength-scale effect of a rock joint/structural surface (CN201410149668.2) and multiple scales rocks shearing machines (CN201310273743.1). They are structurally designed in terms of mounting, transportation, parts protection, testing mechanisms, etc. of multi-scale samples. However, due to the limitation on the test load and the test range of each transducer, each actuator and controller, the requirements on accuracy within a large range of loads cannot be met well by only one loading system. It is very important to develop a direct shear tester assembled by multiple sets of mechanisms for shear strength-scale effect of a rock joint, which is applicable to a large range of loads and provides high accuracy testing results.